The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies are committed to helping those interested in the sciences understand evolution theory and how it can be applied in all areas of scientific research.
This site provides students, teachers and general readers with a variety of learning resources about evolution. It contains important video clips from NOVA and WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It is an emblem of love and unity in many cultures. It can be used in many practical ways in addition to providing a framework for understanding the evolution of species and how they react to changing environmental conditions.
Early attempts to represent the world of biology were built on categorizing organisms based on their metabolic and physical characteristics. These methods, which rely on the sampling of various parts of living organisms or on short fragments of their DNA significantly increased the variety that could be represented in the tree of life2. However, these trees are largely composed of eukaryotes; bacterial diversity is not represented in a large way3,4.
Genetic techniques have significantly expanded our ability to represent the Tree of Life by circumventing the requirement for direct observation and experimentation. Particularly, molecular methods allow us to build trees using sequenced markers, such as the small subunit ribosomal gene.
The Tree of Life has been dramatically expanded through genome sequencing. However there is a lot of diversity to be discovered. This is particularly relevant to microorganisms that are difficult to cultivate and are usually present in a single sample5. A recent study of all known genomes has produced a rough draft of the Tree of Life, including numerous archaea and bacteria that are not isolated and their diversity is not fully understood6.
This expanded Tree of Life is particularly useful in assessing the diversity of an area, assisting to determine whether specific habitats require special protection. The information can be used in a variety of ways, from identifying new treatments to fight disease to improving crop yields. This information is also beneficial for conservation efforts. It helps biologists determine the areas most likely to contain cryptic species with important metabolic functions that may be vulnerable to anthropogenic change. While funds to protect biodiversity are important, the best method to protect the biodiversity of the world is to equip the people of developing nations with the necessary knowledge to act locally and support conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) depicts the relationships between different organisms. Scientists can build an phylogenetic chart which shows the evolutionary relationships between taxonomic groups using molecular data and morphological similarities or differences. Phylogeny plays a crucial role in understanding biodiversity, genetics and evolution.
A basic phylogenetic Tree (see Figure PageIndex 10 Finds the connections between organisms that have similar traits and have evolved from an ancestor that shared traits. These shared traits could be either homologous or analogous. Homologous traits are the same in their evolutionary paths. Analogous traits could appear like they are but they don't share the same origins. Scientists arrange similar traits into a grouping called a clade. For 무료 에볼루션 , all the organisms that make up a clade share the trait of having amniotic eggs and evolved from a common ancestor who had these eggs. A phylogenetic tree is then constructed by connecting the clades to identify the species which are the closest to one another.
Scientists make use of DNA or RNA molecular information to create a phylogenetic chart that is more accurate and precise. This information is more precise than morphological information and provides evidence of the evolutionary history of an individual or group. Researchers can use Molecular Data to calculate the age of evolution of organisms and determine how many organisms have the same ancestor.
Phylogenetic relationships can be affected by a number of factors that include the phenotypic plasticity. This is a type behavior that alters in response to unique environmental conditions. This can cause a trait to appear more similar to one species than another, obscuring the phylogenetic signal. This problem can be addressed by using cladistics. This is a method that incorporates a combination of analogous and homologous features in the tree.
Additionally, phylogenetics aids determine the duration and speed at which speciation occurs. This information can assist conservation biologists in making choices about which species to save from the threat of extinction. In the end, it is the conservation of phylogenetic variety that will lead to an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme of evolution is that organisms acquire various characteristics over time due to their interactions with their environment. Many scientists have proposed theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism would evolve according to its individual requirements as well as the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or absence of certain traits can result in changes that are passed on to the next generation.
In the 1930s and 1940s, theories from a variety of fields -- including genetics, natural selection and particulate inheritance - came together to form the current evolutionary theory, which defines how evolution occurs through the variations of genes within a population, and how those variants change in time as a result of natural selection. This model, which encompasses genetic drift, mutations in gene flow, and sexual selection, can be mathematically described.
Recent developments in the field of evolutionary developmental biology have revealed the ways in which variation can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction and the movement between populations. These processes, as well as others, such as directional selection and gene erosion (changes in frequency of genotypes over time), can lead towards evolution. Evolution is defined by changes in the genome over time and changes in phenotype (the expression of genotypes in an individual).
Incorporating evolutionary thinking into all areas of biology education can improve student understanding of the concepts of phylogeny and evolution. In a study by Grunspan et al. It was demonstrated that teaching students about the evidence for evolution increased their understanding of evolution in an undergraduate biology course. To learn more about how to teach about evolution, please see The Evolutionary Potential in all Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution through looking back, studying fossils, comparing species, and studying living organisms. But evolution isn't just something that happened in the past. It's an ongoing process that is that is taking place today. Viruses reinvent themselves to avoid new drugs and bacteria evolve to resist antibiotics. Animals adapt their behavior as a result of a changing world. The results are often apparent.
However, it wasn't until late 1980s that biologists understood that natural selection can be observed in action as well. The main reason is that different traits can confer the ability to survive at different rates as well as reproduction, and may be passed down from one generation to the next.
In the past, when one particular allele, the genetic sequence that defines color in a group of interbreeding organisms, it could quickly become more prevalent than the other alleles. As time passes, this could mean that the number of moths with black pigmentation could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to track evolutionary change when the species, like bacteria, has a high generation turnover. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples of each are taken regularly, and over fifty thousand generations have been observed.
Lenski's work has demonstrated that mutations can drastically alter the efficiency with the rate at which a population reproduces, and consequently the rate at which it changes. It also shows evolution takes time, something that is difficult for some to accept.
Another example of microevolution is that mosquito genes that confer resistance to pesticides show up more often in populations in which insecticides are utilized. Pesticides create an exclusive pressure that favors those who have resistant genotypes.
The rapidity of evolution has led to a growing recognition of its importance especially in a planet shaped largely by human activity. This includes the effects of climate change, pollution and habitat loss that prevents many species from adapting. Understanding evolution will help us make better decisions regarding the future of our planet and the lives of its inhabitants.